Floating-type magnetic heads for use in hard disc recording-reproduction apparatus must be of smaller size and need to fulfill the requirement that the amount of levitation and the track width be made minuter with higher precision in view of the trend of magnetic recording toward higher density in recent years.
FIG. 6 shows a conventional floating magnetic head of the MIG (Metal-In-Gap) type having a head portion H wherein thin films 19, 19 of ferromagnetic metal, such as Sendust, are formed on opposite sides of a magnetic gap portion G, and a slider portion S made of the same material as the main core of the head portion H integrally therewith. Thus, the magnetic head is formed monolithically.
The magnetic head shown in FIG. 6 is produced by the process illustrated in FIGS. 7 to 12.
With reference to FIGS. 7 and 8, two mirror-finished magnetic substrates 1a, 1b are made, for example, of ferrite and are different in thickness. These substrates have surfaces (to be joined together) which are each formed with track width defining grooves 2, winding grooves 3 and a thin film 19 of Sendust or like ferromagnetic metal.
As shown in FIG. 9, a gap spacer 4 of SiO.sub.2 or like nonmagnetic material is formed over the joint surface of at least one of the substrates, i.e., the substrate 1a. The two substrates 1a, 1b are thereafter fixedly joined to each other to prepare a block 6 by arranging the substrates 1a, 1b face-to-face with their gap forming faces in butting contact with each other, inserting glass rods (not shown) into the winding grooves 3, melting the rods and solidifying the melt to fill the track width defining grooves 2 with glass 5.
The block 6 is then cut into two core blocks 7, 7 as seen in FIG. 10. Further as shown in FIG. 11, a side surface 12 of the core block 7 is grooved except at magnetic gap portions G provided by the gap spacer 4 and the vicinity thereof, and the core block 7 is thereafter ground over the surface 8 thereof to be opposed to media to obtain a predetermined depthwise length d and finish the surface 8 to a mirror surface.
Next as shown in FIG. 12, rail grooves 9 are formed in the surface 8, and the core block is cut into a plurality of core chips 10, 10. In this way, the magnetic head 1 shown in FIG. 9 is completed.
However, the process for producing the above magnetic head 1 has a problem. When to be joined together, the substrates 1a, 1b become inevitably displaced from each other, with the result that it is impossible to give an accurate track width to the magnetic gap portion G.
Recently, therefore, a process is employed wherein grooves for defining the track width are formed in a core block which is prepared by joining two substrates together with a gap spacer provided therebetween and cutting the resulting block. FIG. 13 shows a magnetic head 13 prepared by this production process, and FIGS. 14 to 21 show the process.
FIGS. 14 and 15 show two mirror-finished substrates 1a, 1b made of a magnetic material such as ferrite and different in thickness. The surfaces of these substrates to be joined together are first each formed with winding grooves 3 and a thin film 19 of ferromagnetic metal.
Next as shown in FIG. 16, a gap spacer 4 of SiO.sub.2 or like nonmagnetic material is formed over the joint surface of at least one of the substrates, i.e., of the substrate 1a. The two substrates 1a, 1b are thereafter fixedly joined to each other to prepare a block 6 by arranging the substrates 1a, 1b face-to-face with their gap forming faces in butting contact with each other, inserting glass rods (not shown) into the winding grooves 3, melting the rods and solidifying the molten glass. The block 6 is cut into two core blocks 7, 7 as seen in FIG. 17.
Next as shown in FIG. 18, track width defining grooves 2 are formed in the upper surface of the core block 7, and molten glass 11 is thereafter applied to the upper surface of the core block to cover the grooves 2 as shown in FIG. 19, followed by solidification, whereby the grooves 2 are filled with the glass 11. Subsequently, the glass portion 11 applied over a side surface 12 of the core block 7 is removed by grinding, and the core block side surface 12 is grooved except at magnetic gap portions G and the vicinity thereof as seen in FIG. 20. The core block 7 is then ground over the surface thereof to be opposed to media to obtain a predetermined depthwise length d and finish the surface 8 to a mirror surface.
Next as shown in FIG. 21, rail grooves 9 are formed in the surface 8, and the core block 7 is cut into a plurality of core chips 10, 10. In this way, the magnetic head 13 shown in FIG. 13 is completed.
In the process for producing the magnetic head described, an abrasive wheel having diamond abrasive grains adhered thereto is used for forming the track width defining grooves 2. The abrasive wheel used for machining gives a considerably large width to the track width defining grooves 2, consequently making the magnetic head lower in mechanical strength and unstable in quality and also adversely affecting the amount of levitation. Accordingly, the grooves 2 are filled with the glass 11.
The process for producing the magnetic head 13 of FIG. 13 is free of the problem that the displacement involved in joining the substrates 1a, 1b together impairs the accuracy of the track width of the magnetic gap portion G. However, the abrasive wheel used for forming the track width defining grooves 2 inevitably form slopes 2a, 2a on the grooved side walls as shown in FIG. 22, so that the track width alters from a width Tw2 immediately after the formation of the grooves 2 to a width Tw1 corresponding to the amount d1 of grinding of the surface to be opposed to media. The variation in the track width is indefinite, consequently entailing the problem of impairing the accuracy of the track width. Furthermore, a layer degraded by machining remains in the magnetic head to result in impaired performance. The impairment of performance becomes more pronounced with a decrease in the track width.